Organic solar cell active layer with dicyan imidazole derivative as additive, and preparation method and use thereof

Abstract

The application belongs to the technical field of organic optoelectronic devices, and discloses an active layer of an organic solar cell with a dicyan imidazole derivative as an additive, a preparation method of the active layer and application of the active layer. The active layer of the organic solar cell with the dicyan imidazole derivative as the additive comprises: an electron donor material, the molecular structure of the electron donor material containing a thiophene ring and / or an ester carbonyl; an electron acceptor material, the molecular structure of the electron acceptor material containing a terminal cyano group; and a dicyan imidazole derivative additive PBhDCI, the PBhDCI being distributed at the interface between the electron donor material and the electron acceptor material and constructing an interface crosslinking network through non-covalent interaction. By introducing the dicyan imidazole derivative PBhDCI with a twisted V-shaped configuration as the additive, a non-covalent crosslinking network is constructed at the interface between the electron donor material and the electron acceptor material, and the comprehensive performance of the organic solar cell is significantly improved.

Description

Technical Field

[0001] This invention relates to the field of organic optoelectronic device technology, specifically to an active layer of an organic solar cell using dicyanimidazole derivatives as additives, its preparation method, and its applications. Background Technology

[0002] Organic solar cells (OSCs) are considered one of the next-generation photovoltaic technologies with significant application prospects due to their lightweight, high transparency, thinness, excellent mechanical flexibility, and compatibility with large-area manufacturing. In recent years, with the rapid development of non-fullerene acceptor (NFAs) materials, the photoelectric conversion efficiency (PCE) of single-junction organic solar cells based on bulk heterojunction (BHJ) structures has exceeded 20%.

[0003] However, the long-term operational stability, especially the thermal stability, of organic solar cells remains a key issue restricting their commercial application. Specifically, the active layer of BHJ is thermodynamically metastable. Under thermal stress, the donor and acceptor phase regions are prone to phenomena such as intensified molecular diffusion-driven phase separation and excessive crystallization of components, which disrupt the bicontinuous interpenetrating network morphology on which exciton dissociation and charge transport depend, ultimately leading to irreversible degradation of device performance.

[0004] To improve the thermal stability of the active layer of organic solar cells, additive engineering is one of the most widely adopted strategies. Traditional liquid additives (such as 1,8-diiodooctane (DIO) and 1-chloronaphthalene (CN)) mainly optimize the initial morphology by adjusting the film-forming kinetics during solution processing, but they have almost no inhibitory effect on the thermally induced morphological degradation of the active layer during long-term use. Some solid additives can form molecular locks with donor materials through hydrogen bonding, but these single-function additives can only anchor a single component (donor or acceptor), cannot stabilize the donor-acceptor interface, and the hydrogen bonding force weakens at high temperatures, thus having a limited effect on improving thermal stability.

[0005] In view of this, the present invention is proposed. Summary of the Invention

[0006] The present invention aims to solve at least one of the above technical problems and provides an organic solar cell active layer with dicyanimidazole derivative as an additive, a preparation method thereof and its uses. The present invention can simultaneously anchor two components at the donor-acceptor interface, construct a stable cross-linked network and do not require chemical reaction initiation.

[0007] The first aspect of the present invention provides an active layer for an organic solar cell using a dicyanidazole derivative as an additive.

[0008] A second aspect of the present invention provides an organic solar cell.

[0009] The third aspect of this invention provides a method for preparing organic solar cells.

[0010] The fourth aspect of this invention provides the use of dicyanimidazole derivatives in organic solar cells.

[0011] Compared with the prior art, the present invention has the following beneficial effects: This invention introduces PBhDCI, a dicyanimidazole derivative with a twisted V-shaped molecular configuration, as an additive, which is distributed at the interface between the electron donor and electron acceptor materials. Through non-covalent interactions, an interfacial cross-linking network is constructed, thereby improving the photoelectric conversion efficiency and thermal stability of organic solar cells. Specifically, by optimizing the concentration of PBhDCI, synergistic regulation of efficiency and thermal stability is achieved: when the addition amount is 0.5 wt% of the electron donor material, the photoelectric conversion efficiency reaches 19.7%, and the short-circuit current density increases to 29.8 mA·cm⁻¹. -2 The fill factor reached 77.9%, which was superior to the additive-free control group (efficiency 19.0%, short-circuit current density 29.1 mA·cm). -2 (fill factor 77.1%). When the amount added is increased to 2 wt% of electron donor material, the device exhibits excellent thermal robustness. After continuous thermal aging in a nitrogen environment at 85°C for 50 hours, the photoelectric conversion efficiency is maintained at over 83%, which is much higher than the approximately 52% of the control group. The fill factor and short-circuit current density are maintained at 88.1% and 95.7%, respectively, and the open-circuit voltage decay is controlled within 8%. Attached Figure Description

[0012] Figure 1 The figures shown are characterization diagrams of the chemical structure of the materials and the photovoltaic performance of the devices involved in this invention, wherein: Figure 1 (a) shows the chemical structures of PM6, BTP-eC9, and PBhDCI; Figure 1 (b) JV curves for the initial devices with different PBhDCI contents; Figure 1 (c) shows the EQE spectrum of the corresponding device; Figure 1 (d) JV curves of the corresponding aging devices with different PBhDCI contents; Figure 1 (e) is the normalized PCE evolution of the device during thermal aging at 85°C under a nitrogen atmosphere; Figure 1 (f) is V OC Evolution during the aging process; Figure 1 (g) is J SC Evolution during the aging process; Figure 1 (h) represents the evolution of FF during the aging process; Figure 2The diagram shows the physical performance characteristics of the device of the present invention, wherein: Figure 2 (a) is the initial device J SC Light intensity dependence; Figure 2 (b) is the initial device V OC Light intensity dependence; Figure 2 (c) is the initial device. J ph - V eff curve; Figure 2 (d) is the device after thermal aging. J SC Light intensity dependence; Figure 2 (e) Device after thermal aging V OC Light intensity dependence; Figure 2 (f) shows the device after thermal aging. J ph - V eff curve; Figure 2 (g) represents the TPV decay kinetics of the control group and the 2 wt% PBhDCI device; Figure 2 (h) represents the TPC decay kinetics of the control group and the 2wt% PBhDCI device; Figure 2 (i) Photo-CELIV transients of the control group and the 2 wt% PBhDCI device; Figure 3 These are multi-scale morphology and structural characterization diagrams of the active layer thin film of the present invention, wherein: Figure 3 (a) is the AFM height diagram of the blend film; Figure 3 (b) is a two-dimensional GIWAXS pattern of the corresponding blend film; Figure 3 (c) is a one-dimensional in-plane (IP) GIWAXS line section along the qxy direction; Figure 3 (d) is a two-dimensional GISAXS pattern of the blend film; Figure 3 (e) is a one-dimensional in-plane GISAXS scattering profile along the qxy direction; Figure 4 This is a schematic diagram of the "morphology locking" mechanism achieved by the PBhDCI additive in the active layer of the organic solar cell of the present invention; Figure 5 This diagram serves as a proof of the universality of the invention in other systems, wherein: Figure 5 (a) shows the chemical structure of L8-BO and the normalized PCE evolution of PM6:L8-BO devices with and without 2 wt% PBhDCI during thermal aging at 85°C. Figure 5(b) shows the chemical structure of BTP-4F-P2EH and the normalized PCE evolution of PM6:BTP-4F-P2EH devices with and without 2 wt% PBhDCI during thermal aging at 85°C. Detailed Implementation

[0013] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0014] The first embodiment of the present invention provides an active layer for an organic solar cell using a dicyanimidazole derivative as an additive, comprising: An electron donor material, wherein the molecular structure of the electron donor material contains a thiophene ring and / or an ester carbonyl group; An electron acceptor material, wherein the molecular structure of the electron acceptor material contains a terminal cyano group; The dicyanimidazole derivative additive PBhDCI is distributed at the interface between the electron donor material and the electron acceptor material, and forms an interfacial cross-linking network through non-covalent interactions.

[0015] In this embodiment, the active layer employs a bulk heterojunction. The non-covalent cross-linked network refers to a physically cross-linked structure formed through intermolecular forces such as hydrogen bonds and dipole-dipole interactions, which differs from chemically cross-linked networks connected by covalent bonds. This network can, without breaking covalent bonds, enhance the kinetic barrier of thermally activated molecular diffusion through the synergistic effect of multiple intermolecular forces, thereby suppressing phase coarsening.

[0016] The chemical structure of PBhDCI (see Figure 1 (a) is 4,4'-((propane-2,2-dimethylbis(4,1-phenylene))bis(oxy))dibenzaldehyde dicyandiamide imidazole, whose molecular skeleton contains bisphenol A structural unit (propane-2,2-dimethylbis(4,1-phenylene)). This structure makes the molecule present a twisted V-shaped geometric configuration, which is beneficial for spatial positioning and orientation at the donor-acceptor (DA) interface, and acts as a molecular bridge.

[0017] As an example and not a limitation, the electron donor material is selected from one or more of the formulas (1)-(3): Equation (1) , Equation (2) , Equation (3) ; The electron acceptor material is selected from one or more of the formulas (4)-(10): Equation (4) , Equation (5) , Equation (6) , Equation (7) , Equation (8) , Equation (9) , Equation (10) ; Among them, each of R1, R2, R3, R4, R5, R6, R7, R8, R9, R 10 Each is independently selected from H, C1-C30 alkyl or aryl, C1-C30 alkoxy and C1-C30 alkylthio; each X is independently selected from O, S and Se; each Y is independently selected from H and halogen atoms.

[0018] When the electron donor material contains both a thiophene ring and an ester carbonyl group (such as PM6), PBhDCI can simultaneously form double hydrogen bonds of NH···S and NH···O=C for anchoring; when the electron donor material contains only a thiophene ring or only an ester carbonyl group, PBhDCI anchors the donor through the corresponding single hydrogen bond interaction.

[0019] The interaction mechanism between PBhDCI and the active layer components includes bifunctional anchoring: on the one hand, it forms NH···S hydrogen bonds with the thiophene ring of the electron donor material through the imidazole NH group, and simultaneously forms NH···O=C hydrogen bonds with the ester carbonyl group of the electron donor material; on the other hand, it forms CN···CN dipole-dipole interactions and NH···N≡C hydrogen bonds with the terminal cyano group of the electron acceptor material through the dicyano group. This bifunctional anchoring mechanism allows PBhDCI to simultaneously anchor both the donor and acceptor, acting as a molecular bridge at the interface to construct a dense non-covalent cross-linked network, thereby increasing the kinetic barrier for thermally activated molecular diffusion and effectively suppressing phase coarsening during thermal aging.

[0020] Based on the mass of the electron donor material, the content of PBhDCI can range from 0.5 wt% to 2 wt%. This content range was determined based on systematic concentration optimization experiments, covering the complete controllable range from optimizing initial efficiency to optimizing thermal stability. As a key improvement, adjusting this concentration allows for stepwise optimization of device performance: lower concentrations (e.g., 0.5 wt%) primarily optimize photoelectric conversion efficiency, while higher concentrations (e.g., 2 wt%) primarily optimize thermal stability. This concentration-dependent stepwise optimization effect reflects the unique mechanism by which additives play a role in the efficiency-stability tradeoff.

[0021] The ratio of electron donor to electron acceptor materials and the solution concentration can be routinely optimized and adjusted according to the specific material combination, coating process, and target device performance. The weight ratio of electron donor to electron acceptor materials is usually determined through system optimization. Taking the PM6 and BTP-eC9 system as an example, an experimentally optimized weight ratio of 1:1.2 was determined. This ratio can form a suitable donor-acceptor bicontinuous interpenetrating network, balancing exciton dissociation efficiency and charge transport efficiency. When the electron acceptor material is replaced with other non-fullerene acceptors containing terminal cyano groups (such as L8-BO, BTP-4F-P2EH), those skilled in the art can make routine fine-tuning around this ratio (e.g., adjusting to 1:1.0 or 1:1.3) based on photovoltaic efficiency feedback, according to the differences in acceptor crystallinity, to obtain the optimal phase separation morphology. This ratio optimization based on efficiency feedback is a conventional technique in this field. The concentration of the electron donor material is usually optimized in conjunction with coating process parameters. For example, a PM6 concentration of 7.5 mg·mL⁻¹ is used. -1 For example, this concentration, combined with a spin coating speed of 3000 rpm, can achieve an active layer thickness of approximately 100 nm, balancing sufficient visible light absorption and effective charge transport. By using different spin coating speeds (such as 2500 rpm or 3500 rpm) or by switching to large-area coating processes such as blade coating or slot coating, those skilled in the art can achieve concentrations of 6-9 mg·mL through routine experiments. -1 Fine-tuning is performed within a certain range to obtain a target film thickness of 80-120 nm. This concentration adjustment based on coating process conditions is a standard process optimization practice.

[0022] A second embodiment of the present invention provides an organic solar cell, including the organic solar cell active layer with dicyanimidazole derivatives as additives as described in the first embodiment. Specifically, the cell adopts a conventional device structure, including a transparent conductive substrate, a hole transport layer, an active layer, an electron transport layer, and a metal electrode stacked sequentially.

[0023] As an example and not a limitation, the transparent conductive substrate may be ITO (indium tin oxide), the hole transport layer may be PEDOT:PSS, the electron transport layer may be PDINN, and the electrode may be a silver electrode. The active layer comprises an electron donor material PM6, an electron acceptor material BTP-eC9, and an additive PBhDCI, wherein PBhDCI constructs a non-covalent cross-linked network at the interface between the electron donor and electron acceptor materials.

[0024] This organic solar cell achieves a synergistic improvement in efficiency and thermal stability by introducing PBhDCI additive. When the PBhDCI content in the active layer is 0.5 wt% (based on electron donor mass), the cell can achieve a photoelectric conversion efficiency of approximately 19.7%; when the content is 2 wt%, the cell retains more than 80% of its efficiency after 50 hours of thermal aging at 85°C under nitrogen atmosphere.

[0025] The third embodiment of the present invention provides a method for preparing an organic solar cell, comprising: The dicyanimidazole derivative additive PBhDCI is dissolved in an organic solvent with an electron donor material and an electron acceptor material, and stirred to form an active layer solution. The molecular structure of the electron donor material contains a thiophene ring and / or an ester carbonyl group, and the molecular structure of the electron acceptor material contains a terminal cyano group. The active layer solution is coated onto the substrate by solution processing and then thermally annealed to form an active layer, wherein PBhDCI is distributed at the interface between the electron donor material and the electron acceptor material, and an interfacial cross-linking network is constructed through non-covalent interactions.

[0026] As an example, the preparation method may include: cleaning, drying, and treating the ITO substrate with ultraviolet-ozone (UV-Ozone); spin-coating a PEDOT:PSS solution onto the pretreated ITO substrate surface and annealing to form a hole transport layer; co-dissolving electron donor materials, electron acceptor materials, and PBhDCI in chloroform and stirring at 50-60°C in the dark for 1 hour to obtain an active layer solution; spin-coating the active layer solution onto the hole transport layer surface and annealing at 100°C for 3-5 minutes to form the active layer; spin-coating a PDINN methanol solution onto the active layer surface to form an electron transport layer; and thermally evaporating a silver electrode onto the electron transport layer surface under high vacuum to obtain an organic solar cell device.

[0027] The fourth embodiment of the present invention provides the use of a dicyanimidazole derivative in organic solar cells, wherein the dicyanimidazole derivative is PBhDCI, and is used as an additive to construct a non-covalent crosslinked network at the interface between an electron donor material and an electron acceptor material; wherein the electron donor material comprises a thiophene ring and / or an ester carbonyl group, and the electron acceptor material comprises a terminal cyano group.

[0028] PBhDCI plays a dual role in organic solar cells: on the one hand, it improves the initial photoelectric conversion efficiency by optimizing the morphology of the active layer; on the other hand, it improves the long-term operational stability of the device by constructing a non-covalent crosslinked network to suppress thermally induced phase coarsening.

[0029] Specifically, PBhDCI, through its twisted V-shaped molecular configuration, acts as a molecular bridge at the donor-acceptor interface: it anchors to the donor by forming NH···S hydrogen bonds with the thiophene ring of the electron donor material via the imidazole NH group, and / or NH···O=C hydrogen bonds with the ester carbonyl group of the electron donor material; and it anchors to the acceptor by forming CN···CN dipole-dipole interactions and NH···N≡C hydrogen bonds with the terminal cyano group of the electron acceptor material via dicyano groups. This bifunctional anchoring mechanism constructs a dense non-covalent cross-linked network, significantly increasing the kinetic barrier for thermally activated molecular diffusion, thereby suppressing phase coarsening of the bulk heterojunction active layer under thermal stress.

[0030] This application has been validated in various PM6-based blends, demonstrating its broad applicability to stabilizing the BHJ morphology of electron acceptor materials containing terminal cyano groups, and providing a simple and universal method for solving the thermal stability problem of organic solar cells.

[0031] The following examples illustrate in detail the preparation and performance of the active layer of an organic solar cell using dicyanimidazole derivatives as additives.

[0032] The PBhDCI used in this invention was synthesized according to methods disclosed in the prior art, such as Z. Zhu et al., Dicyanoimidazole resin with bisphenol A moiety: Synthesis, processing, properties, and composites, Journal of Applied Polymer Science, 2022, 140, e53499.

[0033] Example 1: Fabrication and performance characterization of organic solar cells with different PBhDCI contents This embodiment provides a complete device fabrication method including an organic solar cell active layer, and studies the effects of different PBhDCI addition amounts (0, 0.5wt%, 1wt%, 2wt%) on the photovoltaic performance and thermal stability of the device. All devices adopt a conventional structure: ITO / PEDOT:PSS / PM6:BTP-eC9 active layer / PDINN / Ag.

[0034] 1. Device fabrication process The ITO substrate was sequentially cleaned with detergent, sonicated with deionized water, acetone, and isopropanol, and then treated with UV-Ozone for 20 minutes. A PEDOT:PSS solution (Clevios P ​​VP AI 4083) was spin-coated onto the pre-cleaned ITO substrate at 3000 rpm for 30 seconds, followed by annealing in air at 150°C for 15 minutes. The substrate was then transferred to a nitrogen-filled glove box.

[0035] Using chloroform as a solvent, the electron donor material PM6 and the electron acceptor material BTP-eC9 were blended at a mass ratio of 1:1.2, wherein the concentration of PM6 was 7.5 mg·mL⁻¹. -1 For the modified devices, 0.5 wt%, 1 wt%, and 2 wt% PBhDCI were added based on the mass of the electron donor material (the resulting samples are represented as 0.5 wt% PBhDCI, 1 wt% PBhDCI, and 2 wt% PBhDCI, respectively); no PBhDCI was added to the control group. The solutions were stirred at 50°C for 1 hour on a heating stage. The active layer solution was spin-coated at 3000 rpm for 30 seconds, and then heat-annealed at 100°C for 5 minutes.

[0036] PDINN solution (0.5 mg / mL) -1 The solvent (methanol) was spin-coated onto the top of the active layer at 3000 rpm for 30 seconds. Finally, it was subjected to a high vacuum (2 × 10⁻⁶ m³ / s). -4 A 100 nm Ag electrode was thermally evaporated at (Pa). The total active area of ​​the device was 0.04 cm². 2 The mask aperture area is 0.0256 cm². 2 .

[0037] 2. Initial Device Photovoltaic Performance Testing Current density - voltage ( J - V The characteristics of the Enlitech SS-X50 solar simulator under simulated AM 1.5 G illumination (100 mW·cm⁻¹) are demonstrated. -2 Measurements were taken using a Keysight B2900 source meter. Measurements were performed using a forward voltage scan from -0.5 V to 1.2 V, with a step size of 0.02 V and a dwell time of 0.01 s. Light intensity was calibrated to one solar intensity using a certified silicon reference cell. External quantum efficiency (EQE) spectra were acquired using a commercially available Enlitech QE-R system.

[0038] The optimal initial photovoltaic parameters for different PBhDCI contents are shown in Table 1. J - V The curve is shown Figure 1 (b), The EQE spectrum is shown in Figure 1 (c)

[0039] Table 1 In Table 1, a The values ​​in parentheses are statistical data. b J cal It is calculated by the external quantum efficiency (EQE) spectral integral.

[0040] in, V OC Open circuit voltage, J cal The integral current density is derived from the EQE spectrum. J SC The short-circuit current density is given, FF is the fill factor, and the values ​​in parentheses are the mean and standard deviation calculated from eight independent devices. All PBhDCI-modified devices exhibit reproducible photonic response enhancement in the 300–450 nm wavelength range (see [reference]). Figure 1 (c)), compared with the results obtained from JV measurements J SC The value increases are consistent.

[0041] 3. Thermal stability testing and performance characterization after aging Thermal stability was evaluated by aging the packaged devices at 85°C in a nitrogen-filled glove box. The evolution of key photovoltaic parameters was tracked as a function of aging time.

[0042] Figure 1 (d) shows the JV curves of the corresponding aged devices with different PBhDCI contents. Table 2 summarizes the JV curves of PM6:BTP-eC9 devices with different PBhDCI concentrations under AM 1.5G illumination (100 mW cm⁻¹). -2 Photovoltaic performance after 50 hours of thermal aging at 85°C.

[0043] Table 2 .

[0044] Figure 1(e) shows the evolution of the normalized PCE of the devices during thermal aging at 85°C under a nitrogen atmosphere. The control device without PBhDCI exhibited rapid and significant performance degradation, with its normalized PCE decreasing to only about 52% after 50 hours of aging. In contrast, all PBhDCI-modified devices showed significantly improved PCE retention. This improvement directly reflects the protective effect of the non-covalent interfacial crosslinking network formed by PBhDCI: PBhDCI anchors PM6 through N–H···S / O hydrogen bonds on the one hand, and BTP-eC9 through CN···CN / N–H···N interactions on the other hand, thereby effectively enhancing the kinetic barrier for thermally activated molecular diffusion and DA phase coarsening. The device with 2 wt% PBhDCI exhibited the best thermal robustness, retaining about 83% of the initial PCE after 50 hours of sustained thermal stress.

[0045] Figure 1 (f)-(h) show the open-circuit voltages respectively. V OC Short-circuit current density J SC The evolution of the fill factor FF during the aging process. Specifically, after 50 hours of thermal aging, the normalized fill factor (the ratio of the aged FF to the initial FF, FF / FF0) and normalized short-circuit current density (after aging) of the unmodified device are observed. J SC With the initial J SC The ratio, J SC / J SC0 The fill factor and short-circuit current density decreased to 0.722 and 0.779, respectively, corresponding to relative reductions of 27.8% and 22.1%. The device containing 2 wt% PBhDCI exhibited the best thermal robustness, maintaining a fill factor of 88.1% (FF / FF0 = 0.881) and a short-circuit current density of 95.7% after 50 hours of aging. J SC / J SC0 =0.957). In addition, the open-circuit voltage... V OC Relatively stable across all devices (retention rate >92%). The superscript "0" indicates the initial test value of the device in its initial state (before aging), FF / FF0 and... J SC / J SC0 This indicates the performance retention rate after thermal aging.

[0046] 4. Light intensity dependence test ForJ SC / V OC - P light The samples were prepared using the same procedure as those for solar cells. The JV curves of the devices were measured in a glovebox using a Keysight B2901B source meter at solar irradiances of 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, and 100%. The voltage range was -0.5 V to 1.2 V, with a step size of 0.02 V and a delay time of 10 ms. J SC and P light The relationship between them follows a formula J SC ∝ P light α .and V OC and P light The relationship between them follows a formula V OC ∝ (nkT / q) ln( P light ), where n is the ideality factor, k is the Boltzmann constant, T is the absolute temperature, and q is the elementary charge.

[0047] Figure 2 (a) and (b) show the light intensity dependence of the initial devices. In the initial state, all devices exhibit a slope (S) close to 1, but the PBhDCI-doped devices have a slope even closer to 1: the S value for the control device is 0.992, while the S values ​​for the 0.5 wt%, 1 wt%, and 2 wt% PBhDCI devices are 0.998, 0.997, and 0.993, respectively. These results indicate that PBhDCI doping effectively suppresses bimolecular recombination in the active layer, a key contributing factor to the improved FF of the modified initial devices. PBhDCI doping reduces the ideality factor n to a value closer to 1: the n value for the control device is 1.10, while the n values ​​for the 0.5 wt%, 1 wt%, and 2 wt% PBhDCI devices are 1.01, 1.04, and 1.08, respectively. The lower ideality factor implies that PBhDCI acts as an effective trap passivator in the BHJ active layer, reducing the density of interfacial defect states through hydrogen bonding and dipole interactions.

[0048] Figure 2(d) and 2(e) show the light intensity dependence after thermal aging. After thermal aging, the control device showed a significant decrease in the S value to 0.970, which is a sign of increased bimolecular recombination loss. In contrast, all devices containing PBhDCI maintained a slope close to 1 (0.982 for 0.5 wt%, 0.992 for 1 wt%, and 0.993 for 2 wt%). After thermal aging, the n value of the control device increased sharply to 1.35, indicating that thermal stress induced severe trap formation and intensified trap-assisted recombination. Conversely, the PBhDCI-doped devices effectively mitigated this degradation, with n values ​​remaining at 1.29 (0.5 wt%), 1.11 (1 wt%), and 1.13 (2 wt%). Notably, the 1 wt% and 2 wt% PBhDCI devices maintained an ideal factor close to 1, confirming that PBhDCI suppresses the generation of recombination-active trap states during long-term thermal aging.

[0049] 5. J ph - V eff Measurement and exciton dissociation efficiency For J ph - V eff The samples measured were prepared using the same fabrication procedure as those for solar cells. The device's... J L or J D The curve is in the glove box, at AM 1.5G (100 mW cm⁻¹). -2 ) or measured using a Keysight B2901B source meter in the dark. Voltage range: -2 V to 1.2 V. Step size: 0.02 V. Delay time: 10 ms. Exciton dissociation efficiency ( η diss )= J SC / J sat . J sat The saturation photocurrent is obtained through the following calculations: J ph = J L - J D , V eff = V 0− V appl ,in, J ph Photocurrent density, V effFor effective voltage, J L and J D These represent the photocurrent density under illumination and in the dark, respectively. V appl Indicates the applied voltage. V 0 points J L = J D The voltage value at that time. V eff At a voltage >2.3 V, the photogenerated excitons generated in the device can be considered to have been completely collected. J ph Reaching saturation ( J sat ).

[0050] Figure 2 (c) shows the initial device. J ph – V eff curve. Figure 2 (f) shows the results after thermal aging. J ph – V eff The curves show that, for the unmodified control device, the exciton dissociation probability decreased by 13.5% in absolute value after thermal aging (from 98.5% to 85.0%). Doping with 0.5 wt% PBhDCI failed to mitigate the loss of exciton dissociation probability, with the value decreasing to 84.2% after aging. In contrast, increasing the doping content to 1 wt% and 2 wt% significantly improved aging stability: the 1 wt% PBhDCI device maintained a high exciton dissociation probability of 91.6% after aging, while the 2 wt% PBhDCI device showed the best retention, with its exciton dissociation probability decreasing by only 1.1% in absolute value after aging (from 96.2% to 95.1%), far exceeding that of the control device. This indicates that the interfacial crosslinking network effectively retained the DA interface area necessary for exciton dissociation.

[0051] 6. TPC and TPV Measurement The packaged device was used to test transient photocurrent (TPC) and transient photovoltage (TPV). Data were acquired using the Paios (Fluxim AG, Switzerland) integrated characterization platform. In TPC testing, the light intensity was 100%, the pulse length was 100 µs, the settling time was 100 µs, and the tracking time was 200 µs. In TPV testing, the light intensities were 0.10%, 0.21%, 0.44%, 0.95%, 1.95%, 4.10%, 8.62%, 18.11%, 38.06%, and 80.0% of the solar intensity. The pulse length was 5 µs, the settling time was 30 µs, and the tracking time was 30 µs.

[0052] The test samples were divided into four groups: (1) “w / o PBhDCI-Fresh” (pre-aging control group): initial devices without PBhDCI; (2) “w / o PBhDCI-Aged” (post-aging control group): thermally aged devices without PBhDCI; (3) “w / PBhDCI-Fresh” (pre-aging experimental group): initial devices with 2 wt% PBhDCI; (4) “w / PBhDCI-Aged” (post-aging experimental group): thermally aged devices with 2 wt% PBhDCI.

[0053] Figure 2 (g) shows the TPV decay kinetics of the control and 2 wt% PBhDCI devices. The TPV results show that the 2 wt% PBhDCI device before aging has a longer carrier lifetime of 5.10 µs, compared to 4.90 µs for the control device. This extended lifetime confirms that recombination is suppressed in the fresh active layer modified with PBhDCI, directly contributing to the improved charge-free efficiency (FF). After aging, the carrier lifetime of the control device drops sharply to 3.82 µs, while the 2 wt% PBhDCI device maintains a high lifetime of 4.86 µs. The decay is negligible, demonstrating that PBhDCI effectively suppresses the increase in charge recombination caused by aging.

[0054] Figure 2 (h) shows the TPC decay kinetics of the control and 2 wt% PBhDCI devices. TPC characterization revealed that the 2 wt% PBhDCI device before aging had a charge extraction time of 0.266 µs, almost identical to the 0.267 µs of the control device before aging. This result indicates that the incorporation of PBhDCI did not disrupt the charge extraction pathway but maintained efficient extraction kinetics in the initial device, which is crucial for maintaining high FF. After aging, the extraction time of the control device increased significantly to 0.328 µs, while the 2 wt% PBhDCI device maintained rapid and stable extraction kinetics, increasing only slightly to 0.273 µs.

[0055] 7. Photo-CELIV Measurement of Linear Charge Extraction Photo-CELIV measurements further quantified the charge mobility of the device. Figure 2 (i) shows the photo-CELIV transients of the control group and the 2 wt% PBhDCI device. Prior to aging, the charge mobility of the 2 wt% PBhDCI device was 2.45 × 10⁻⁶. -4 cm 2 V -1 s -1 This is significantly higher than the 1.81 × 10⁻⁶ of the control device before aging. -4 cm 2 V -1 s -1 The improved mobility indicates that PBhDCI optimizes the charge transport channels in the active layer, reduces charge transport losses, and contributes to improving the device's flyback effect (FF). J SC After initial device aging, the mobility of the control device decreased to 1.28 × 10⁻⁶. -4 cm 2 V -1 s -1 Meanwhile, the 2 wt% PBhDCI device maintained 2.52 × 10⁻⁶. -4 cm 2 V -1 s -1 The results demonstrate that the non-covalent interfacial network effectively protects the charge transport pathway from thermal degradation. These results, combined with the above device physical characterization, confirm that PBhDCI optimizes the charge generation, transport, and extraction processes of the initial device, achieving high mobility. J SC The synchronous improvement of FF improves PCE; on the other hand, it effectively suppresses charge dynamics degradation caused by thermal aging and improves the thermal stability of the device.

[0056] 8. Morphological characterization (AFM, GIWAXS, GISAXS) Atomic force microscopy (AFM) measurements were performed using a Bruker Dimension Icon in tapping mode with an SCM-PIT-V2 scanning probe. Figure 3(a) shows the AFM height map of the blended films (scan size: 2 µm × 2 µm). The test samples were divided into four groups: w / o PBhDCI Fresh (before aging) represents the initial film without PBhDCI (control group before aging), w / o PBhDCI Aged (after aging) represents the thermally aged film without PBhDCI (control group after aging), w / PBhDCI Fresh (before aging) represents the initial film with 2 wt% PBhDCI (experimental group before aging), and w / PBhDCI Aged (after aging) represents the thermally aged film with 2 wt% PBhDCI (experimental group after aging).

[0057] After aging, the root mean square roughness (Rq) of the control group film (w / o PBhDCI) increased significantly from 0.794 nm to 1.03 nm. In contrast, the roughness of the experimental group film containing 2 wt% PBhDCI (w / PBhDCI) changed less (from 1.11 nm to 1.23 nm, an increase of approximately 10.8%), indicating that the interfacial crosslinking network effectively limited the rearrangement of surface morphology during thermal aging.

[0058] Grazing-incidence wide-angle X-ray scattering (GIWAXS) data were acquired at the BL02U2 beamline of the Shanghai Synchrotron Radiation Facility (SSRF). The monochromatic source wavelength was 1.24 Å (10 keV). Data were recorded using a two-dimensional Pilatus 2M image board detector (Dectris, Switzerland). Figure 3 (b) shows the two-dimensional GIWAXS pattern of the corresponding blend film. Figure 3 (c) shows the path along q xy One-dimensional in-plane (IP) GIWAXS cross-sections in the direction of thermal aging. In the out-of-plane (OOP) direction, the binary films exhibit an aging-induced shift in the π-π packing peak: the π-π packing distance decreases from 3.67 Å (before aging) to 3.63 Å (after aging), while the coherence length (CCL) slightly increases from 36.7 Å to 38.1 Å. In contrast, the film containing 2 wt% PBhDCI shows a small change in OOP molecular packing after aging, maintaining an almost constant π-π packing distance (≈3.61 Å) and CCL (≈37.7 Å). In the in-plane (IP) direction, both groups of films show a decrease in CCL after thermal aging; more importantly, the magnitude of CCL decay in the PBhDCI-modified film (from 201.4 Å to 185.3 Å) is significantly smaller than that in the binary film (from 223.6 Å to 194.5 Å), which further supports the stabilizing effect of PBhDCI at the molecular level.

[0059] Grazing-incidence small-angle X-ray scattering (GISAXS) experiments were conducted at the BL05U beamline of the Hefei Light Source (HLS). Samples were prepared on silicon substrates using the same processing conditions as the active layer of the device. The incident angle was set to 0.2°. The intensity of the scattered X-rays was recorded using a two-dimensional detector. Figure 3 (d) shows the two-dimensional GISAXS pattern of the blended film. Figure 3 (e) shows the path along q xy One-dimensional in-plane GISAXS scattering profiles with corresponding model fitting curves are generated. The one-dimensional distribution profiles are extracted from horizontal slices of two-dimensional GISAXS patterns and analyzed using the Debye-Anderson-Brumberger (DAB) model combined with fractal structure factors to determine domain size and associated length.

[0060] Table 3 summarizes the detailed structural parameters of PM6:BTP-eC9 blend films before and after aging, with and without (w / o) 2 wt% PBhDCI, extracted from the GISAXS profile.

[0061] Table 3 Where ξ is the characteristic correlation length of the PM6-rich domain, η is the correlation length of the BTP-eC9-rich phase, and R g Let 2R be the radius of gyration. g Let be the acceptor aggregate size derived from the radius of gyration, and D be the fractal dimension. These structural parameters confirm that PBhDCI effectively suppresses thermally induced phase coarsening while maintaining a balanced domain size distribution and a highly interpenetrating acceptor-donor network.

[0062] As shown in Table 3, thermal aging induced severe morphological degradation in the control film without PBhDCI. The relevant length ξ of the donor-rich domain increased sharply from 13.8 nm before aging to 36.8 nm after aging, indicating severe thermally driven phase coarsening. Simultaneously, the acceptor aggregate size 2Rg increased from 52.3 nm to 74.7 nm, and η increased from 11.7 nm to 16.2 nm. This collective evolution of structural parameters reflects uncontrolled phase separation in the aged binary film, consistent with the significant FF degradation observed in the control device. In contrast, the film containing 2 wt% PBhDCI showed a significantly restricted morphological evolution during aging. Specifically, ξ increased moderately (from 15.3 nm to 25.1 nm), 2Rg only slightly increased (from 59.7 nm to 67.9 nm), and η moderately increased (from 13.8 nm to 15.2 nm). The variation range of all structural parameters was significantly smaller than that of the control film, demonstrating that PBhDCI effectively suppressed thermally induced phase coarsening while maintaining a balanced domain size distribution and a highly interpenetrating donor-acceptor network. This stable nanomorphology, coupled with the high exciton dissociation probability observed after thermal aging of PBhDCI-modified devices (95.1% for 2 wt% PBhDCI-aged devices compared to 85.0% for aged control devices) and minimal [missing information], further supports this conclusion. J SC / FF loss is directly related.

[0063] 9. Schematic diagram of topography locking mechanism Figure 4 This diagram schematically illustrates the morphology-locking mechanism achieved by PBhDCI in the active layer of an organic solar cell, where w / o PBhDCI represents the film without PBhDCI and w / PBhDCI represents the modified film containing PBhDCI. PBhDCI, exhibiting a distorted V-shaped geometry, is preferentially distributed at the DA interface, acting as a molecular bridge. It anchors the PM6 donor chain through NH···S hydrogen bonds (with the PM6 thiophene ring) and strong NH···O=C hydrogen bonds (with the PM6 ester carbonyl group), while simultaneously tethering the BTP-eC9 acceptor aggregate through strong CN···CN dipole-dipole interactions and NH···N≡C hydrogen bonds (with the BTP-eC9 cyano end group). The formation of this dense interfacial non-covalent crosslinked network significantly enhances the kinetic barrier for thermally induced molecular diffusion and phase coarsening. Therefore, the modified film containing PBhDCI effectively suppresses excessive phase separation during thermal aging and maintains a well-interpenetrating dual continuous network with stable domain size during thermal aging, ensuring the long-term retention of charge generation and transport paths.

[0064] Example 2: Application Verification in the PM6:L8-BO System The device was fabricated according to the method of Example 1, except that the electron acceptor material was replaced with L8-BO instead of BTP-eC9 (chemical structure see...). Figure 5 (a) The PBhDCI content is 2wt% (based on the mass of the electron donor material).

[0065] After 72 hours of thermal aging in a nitrogen atmosphere at 85°C, the PM6:L8-BO control device (without PBhDCI) retained only about 51% of the initial PCE, while the PM6:L8-BO device modified with 2wt% PBhDCI retained about 82% of the initial PCE (see [link to product description]). Figure 5 (a) The PCE retention rate increased by approximately 31 percentage points.

[0066] Example 3: Application Verification in the PM6:BTP-4F-P2EH System The device was fabricated according to the method of Example 1, except that the electron acceptor material was replaced by BTP-4F-P2EH (chemical structure see...). Figure 5 (b) The PBhDCI content is 2wt% (based on the mass of the electron donor material).

[0067] After 72 hours of thermal aging in a nitrogen atmosphere at 85°C, the PM6:BTP-4F-P2EH control device (without PBhDCI) retained only about 76% of the initial PCE, while the 2wt% PBhDCI modified device retained about 86% of the initial PCE (see [link to product description]). Figure 5 (b)), which increased by about 10 percentage points.

[0068] The results clearly demonstrate that this high Tg additive strategy is not limited to the PM6:BTP-eC9 system, but has broad applicability for stabilizing the BHJ morphology of various non-fullerene acceptor (NFA) based OSCs and improving their thermal robustness.

[0069] The above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this application.

Claims

1. An organic solar cell active layer using dicyanimidazole derivatives as additives, characterized in that, include: An electron donor material, wherein the molecular structure of the electron donor material contains a thiophene ring and / or an ester carbonyl group; An electron acceptor material, wherein the molecular structure of the electron acceptor material contains a terminal cyano group; The dicyanimidazole derivative additive PBhDCI is distributed at the interface between the electron donor material and the electron acceptor material, and forms an interfacial cross-linking network through non-covalent interactions.

2. The organic solar cell active layer using dicyanimidazole derivatives as additives as described in claim 1, characterized in that, The PBhDCI forms hydrogen bonds with the thiophene ring and / or ester carbonyl group of the electron donor material through the imidazole NH group, and simultaneously forms dipole-dipole interactions and hydrogen bonds with the terminal cyano group of the electron acceptor material through the dicyano group.

3. The active layer of an organic solar cell using a dicyanimidazole derivative as an additive as described in claim 1, characterized in that, The electron donor material is selected from one or more of the formulas (1)-(3): Equation (1) , Equation (2) , Equation (3) ; The electron acceptor material is selected from one or more of the formulas (4)-(10): Equation (4) , Equation (5) , Equation (6) , Equation (7) , Equation (8) , Equation (9) , Equation (10) ; Among them, R1, R2, R3, R4, R5, R6, R7, R8, R9, R 10 Each is independently selected from H, C1-C30 alkyl or aryl, C1-C30 alkoxy and C1-C30 alkylthio; each X is independently selected from O, S and Se; each Y is independently selected from H and halogen atoms.

4. The active layer of an organic solar cell using a dicyanimidazole derivative as an additive as described in claim 1, characterized in that, Based on the mass of the electron donor material, the content of PBhDCI is 0.5 wt%-2 wt%.

5. The active layer of an organic solar cell using a dicyanimidazole derivative as an additive as described in claim 1 or 4, characterized in that, When the PBhDCI content is 0.5 wt% of the electron donor material, the active layer is used to obtain a device with a photoelectric conversion efficiency ≥19%; when the PBhDCI content is 2 wt% of the electron donor material, the active layer is used to obtain a device with an efficiency retention rate ≥80% after thermal aging at 85°C for 50 hours in a nitrogen atmosphere.

6. An organic solar cell, characterized in that, Includes the active layer as described in any one of claims 1-5.

7. A method for preparing an organic solar cell, characterized in that, include: The dicyanimidazole derivative additive PBhDCI is dissolved in an organic solvent with an electron donor material and an electron acceptor material, and stirred to form an active layer solution. The molecular structure of the electron donor material contains a thiophene ring and / or an ester carbonyl group, and the molecular structure of the electron acceptor material contains a terminal cyano group. The active layer solution is coated onto the substrate by solution processing and then thermally annealed to form an active layer. The PBhDCI is distributed at the interface between the electron donor material and the electron acceptor material, and an interfacial cross-linking network is constructed through non-covalent interactions.

8. The method for preparing an organic solar cell as described in claim 7, characterized in that, Based on the mass of the electron donor material, the content of PBhDCI is 0.5 wt%-2 wt%. The photoelectric conversion efficiency and thermal stability of the device are optimized by adjusting the concentration of PBhDCI.

9. The method for preparing an organic solar cell as described in claim 7, characterized in that, The electron donor material is selected from one or more of the formulas (1)-(3): Equation (1) , Equation (2) , Equation (3) ; The electron acceptor material is selected from one or more of the formulas (4)-(10): Equation (4) , Equation (5) , Equation (6) , Equation (7) , Equation (8) , Equation (9) , Equation (10) ; Among them, R1, R2, R3, R4, R5, R6, R7, R8, R9, R 10 Each is independently selected from H, C1-C30 alkyl or aryl, C1-C30 alkoxy and C1-C30 alkylthio; each X is independently selected from O, S and Se; each Y is independently selected from H and halogen atoms.

10. The use of dicyanimidazole derivatives in organic solar cells, characterized in that, The dicyanimidazole derivative is PBhDCI, which is used as an additive to construct a non-covalent cross-linked network at the interface between the electron donor material and the electron acceptor material; wherein the electron donor material comprises a thiophene ring and / or an ester carbonyl group, and the electron acceptor material comprises a terminal cyano group.

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